Loop of Henle - Kidneys

[snezka18]

Hopefully someone can help me hopefully
I really didnt get my grips with the Loop of henle what is its purpose? is it to maintain osmolality of the interstitial fluid of the medulla, so that they are kinda exchanging salts and water and is that the purpose of urea, to go into the medulla to maintain the osmolality of the medulla...but what is the purpose of that then? What is the purpose of Loop of Henle
Where is Loop of henle permeable to urea, is it in the ascending limb? and then collecting duct is permeable to urea as well?

[Babybel56]

I think I answered the permeability question in the other post. The purpose of the loop of henle is to create a high osmolarity in the renal medulla. A high osmolarity means that water will be induced to leave and concentrate the urine in the collecting ducts that loop back into the medulla.